Interrupting device having u-shaped parallel current paths



May 27, 1969 w. E. HARPER ETAL 3,446,923

INTERRUPTING DEVICE HAVING USHAPED PARALLEL CURRENT PATHS Filed Oct.

Sheet 8. 94301 @11 2 23;? JQI 1" Q L gig-8 -SHAPED PARALLEL CURRENT waslfl -Z- w. E. HARPER ETA!- Jon 2: 7

INTERRUPTYING DEVICE HAVING u Filed'Oct.

May 27, 1969 May 27, 1969 w, HARPER ETAL 3,446,928

INTERRUPTING DEVICE HAVING U-SHAPED PARALLEL CURRENT PATHS Fild Oct. 20,1965 Sheet 3 era J02 L; 145 L 104 gi /l9- 4 1. I: M1 m if! I I 14/ L, 914.9 14/ United States Patent US. Cl. 200-146 3 Claims ABSTRACT OF THEDISCLOSURE There is disclosed an oil circuit breaker having a pair ofspaced apart line terminals extending into the top of a tank containingoil. When the circuit breaker is in closed condition, two U-shapedparallel current paths are established between the line terminals. Theexterior U-shaped current path comprises one or more pairs of separablemain contacts. The interior (and exterior U-shaped current pathcomprises one or more pairs of separable auxiliary contacts. The circuitbreaker is arranged so that the contacts in the interior circuit openfirst and close last as regards the contacts in the exterior circuit.The disposition, length and inductance of the two U-shaped current pathsis such that more current tends to flow in the interior circuit becauseof magnetic eflects caused by current flow through each U- shaped path.The separable contacts in both U-shaped current paths are housed insuitable arc interrupting devices which are supported by upper,intermediate and lower heat dissipating platforms. Impedance devices,such as resistors, associated with the contacts are also supported bythe platforms.

This invention relates generally to electric circuit breakers andparticularly to oil circuit breakers of the fluid blast type, althoughnot necessarily limited thereto.

Some oil circuit breakers comprise one pair or a plurality of seriesconnected pairs of separable contacts for each phase or line of acircuit being protected. In practice each pair of contacts is adapted tooperate inside the housing of an arc interrupting device 'which confinesthe arc formed between the contacts. Usually, fluid blast means areprovided in the housing to aid in extinguishing the arc.

In one well known type of oil circuit breaker a pair of spaced apartline terminals extend into the top of a tank containing a body of fluidsuch as oil and a pair of main arc extinguishing devices are submergedin the fluid. Each main arc extinguishing device comprises an arcconfining housing in which a stationary contact is mounted and thelatter is connected to one of the line terminals. A reciprocably movableelectrically conductive cross arm is located inside the tank and isprovided with a pair of spaced apart bayonet type movable main contacts.Each movable contact is adapted to cooperate with the stationary contactWithin the housing of one of the main arc extinguishing devices. Thus,when the circuit breaker is closed a U-shaped current path or circuit isestablished between the line terminals.

In some circuit breakers of this type, four or more main arcextinguishing devices are used instead of the two described but theU-shaped current path retains its identity.

It is an object of the present invention to increase the continuous andshort circuit current carrying capacity of such circuit breakers bymeans which economically exploit the design and inherent operatingcharacteristics thereof.

Another object is to increase both the normal and short circuit carryingcapacity of such circuit breakers 3,446,928 Patented May 27, 1969 ice byproviding an additional or second current carrying circuit in parallelwith the aforementioned or first U- shaped circuit.

Another object is to locate the second circuit with respect to the firstcircuit so that electromagnetic forces interacting between the twocircuits cause a large proportion of continuous current to flow throughthe second circuit.

Another object is to provide a second circuit which comprises one ormore pairs of auxiliary contacts connected in shunt with the maincontacts in the main arc interrupters and located generally on theinside of the first U-shaped circuit.

Another object is to have the auxiliary contacts open before and closeafter the main contacts so that the main burden of arc interruption ishandled by the main contacts.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustrate several preferred embodiments ofthe invention but it is to be understood that the embodimentsillustrated are susceptible of modifications with respect to detailsthereof without departing from the scope of the appended claims.

In the drawings:

FIG. 1 is an elevational view, partly in section, of one embodiment ofan oil circuit breaker employing the present invention.

FIG. 2 is a top plan view of a portion of the circuit breaker takenalong line IIII of FIG. 1;

FIG. 3 is a cross sectional view of an auxiliary contact structure orare extinguishing device shown in FIG. 1, showing it in open position;

FIG. 4 is a view similar to FIG. 3 but shows the auxiliary contactstructure in closed position;

FIGS. 5, 6 and 7 are diagrammatic showings of a portion of the electriccircuitry of the circuit breaker shown in FIGS. 1 and 2, and show it inclosed, partially open, and fully open positions, respectively; and

FIG. 8 is a diagrammatic showing of another embodiment of an oil circuitbreaker employing the present invention.

Referring to FIG. 1, there is shown an oil circuit breaker incorporatingthe present invention and having a tank 10 which is filled to a level 12with an arc extinguishing fluid such as oil. A pair of line terminalbushings 14 and 16 comprising electrical conductors 18 and 20,respectively, for connection to a power line being protected extend intotank 10. Arc extinguishing assemblies 22 and 24 are suspended from theinner ends of the terminal bushings 14 and 16, respectively. The assemblies 22 and 24 are understood to be similar to each other,therefore, only the former will be described in detail.

Referring to FIGS. 1 and 2, assembly 22 comprises upper, intermediateand lower electrically conductive platform castings 26, 28 and 30,respectively. Upper casting 26 is electrically and mechanicallyconnected to conductor 18 of terminal bushing 14. Intermediate cast ing28 is spaced from and mechanically supported on upper casting 26 bymeans of insulating supports such as support 32. Lower casting 30 isspaced from and mechanically supported on intermediate casting 28 bymeans of insulating supports which are understood to be similar tosupport 32.

Upper and lower main arc interrupters 36 and 38 depend from the upperand intermediate castings 26 and 28, respectively, and, as FIGS. 5, 6and 7 show, comprise stationary contacts 40 and 42, respectively, whichare electrically connected to the upper and intermediate castings,respectively. Reference may be had to Patent Number 3,067,307 for FluidBlast Interrupting Device for Oil Circuit Breakers issued Dec. 4, 1962to J. M.

Ramrath and assigned to the same assignee as the present application fora detailed description of an interrupter of a type suitable forapplication as the main arc interrupters herein referred to.

Upper and lower auxiliary contact structures 44 and 46 are mountedadjacent the main interrupters 36 and 38, respectively, and, as FIGS. 5,6 and 7 show, comprise stationary contacts 48 and 50, respectively,which are electrically connected to the upper and intermediate castings26 and 28, respectively.

Upper auxiliary contact structure 44 is similar to lower auxiliarycontact structure 46, therefore, only the former will be described indetail. As FIG. 3 shows, contact structure 44 comprises a metallic topsection 100 adapted for electrical and mechanical connection to upperplatform casting 26. Top section 100 is provided with oil refill ports102 in the side walls thereof. Adome shaped piston 104 is located withintop section 100 and is provided with openings 106 for equalizing oilpressure on each side thereof and with a vent 108 through the topthereof. Piston 104 is provided with a piston ring 105. A nonmetallicpiston push rod 110 has one end bearing against piston 104 and its otherend abutting against a movable auxiliary contact 78, hereinafterdescribed. Push rod 110 is adapted to maintain vent 108 closed when itbears against piston 104. A push rod driving spring 112 is disposedbetween a portion of top section 100 and push rod 110. A piston drivingspring 114 is disposed between a portion of top section 100 and piston104. Stationary contact 48 which is located in contact structure 44comprises a contact housing 116 in which a cluster of spring biasedcontact fingers 118 are located. Contact housing 116 comprises a spidersection 120 which adapts it for electrical and mechanical connection totop section 100. The lower end of top section 100 is closed by aninsulating bafile plate 122 having a hole 124 for accommodating movableauxiliary contact 78.

High ohmic value resistors 52 and 54 are electrically connected,respectively, between the upper and intermediate castings 26 and 28 andbetween the intermediate and lower castings 28 and 30.

An electrically conductive cross bar 56 which is reciprocably movablevertically (with respect to FIG. 1) by an insulating rod 57 is providedat its extreme ends with upwardly projecting or bayone type electricallyconductive movable contacts and movable contact operators, hereinafterdescribed. Preferrably, cross bar 56 comprises two separate members 5611and 56b to enhance thermal conductivity therefrom. The end of cross bar56 which is associated with are extinguishing assembly 22 comprises amovable lower main contact 58 and a movable lower auxiliary contact 60and a pair of contact operators 62 and 64.

Lower casting 30 of assembly 22 is provided with a pair of slidingcontacts 66 for accommodating the movable contacts 58 and 60. Lowercasting 30 is also provided with a pair of openings 68 in alignment withthe contact operators 62 and 64. The contact operators 62 and 64cooperate with electrically nonconductive contact push rods 72 and 74,respectively. The push rods 72 and.74 are connected to and operate areciprocably movable upper main contact 76 and a reciprocably movableauxiliary upper auxiliary contact 78, respectively, which extend througha pair of sliding contacts 80 and 81, respectively, mounted onintermediate casting 28. Contacts 76 and 78 extend into main arcinterrupter 36 and auxiliary contact structure 44, respectively, whenthe circuit breaker is closed.

Push rod 72 and its attached movable upper main contact 76 are enclosedin an insulated housing 79 shown in FIG. 1 and suitable biasing means,such as a spring 83, in housing 79 tend to bias the push rod and uppermain contact downwardly with respect to FIG. 1. It is to be understoodthat similar provisions are made for housing 4. and biasing the otherpush rods and their attached movable upper contacts.

When the circuit breaker is fully closed, as shown in FIGS. 1 and 5,there are two parallel U-shaped current paths between the conductros 18and 20 of the terminal bushings 14 and 16, respectively, with one pathbeing located substantially within the other.

The outer and longer path extends from conductor 18, through uppercasting 26, stationary contact 40 of upper main interrupter 36, movablecontact 76, intermediate casting 28, stationary contact 42 of lower maininterrupter 38, movable contact 58, cross arm 56, movable contact 58a,stationary contact 42a of lower main interrupter 38a, intermediatecasting 28a, movable contact 76a, stationary contact 40a of upper maininterrupter 36a, upper casting 26a, to conductor 20.

The inner and shorter path extends from conductor 18, through uppercasting 26, stationary contact 48 of upper auxiliary contact structure44, movable contact 78, intermediate casting 28, stationary contact 50of lower auxiliary contact structure 46, movable contact 60', cross arm56, movable contact 60a, stationary contact 50a of lower auxiliarycontact structure 46a, intermediate casting 28a, movable contact 78a,stationary contact 48a of upper auxiliary contact structure 44a, uppercasting 26a, to conductor 20.

No substantial current flows through the impedances 52, 54, 52a or 54awhen the circuit breaker is closed.

Current flow through both paths is accompanied by generation of amagnetic field around each path and these magnetic fields interact tocause a large portion of the current flow through the circuit breaker totravel through the inner path hereinbefore described. More specifically,the outer path is longer than the inner path and therefore has greaterinductance and the larger portion of current will flow through theshorter inner path. Since the inner path includes the auxiliary contactstructures which are adapted to be more readily cooled by the oil in thecircuit breaker than the main interrupters, larger currents can becarried by the inner path than would otherwise be the case if the samecurrent were channeled through the outer path.

FIG. 8 shows another embodiment of the invention wherein only one pairof main ar-c interrupters 36b and 36c and one pair of auxiliary contactstructures 44b and 440 are employed in a circuit breaker. The maininterrupter and auxiliary contact structures shown in FIG. 8 areunderstood to be similar to the corresponding structures hereinbeforedescribed in connection with FIGS. 1-7. Main arc interrupters 36b and36c comprise stationary main contacts 40b and 400, respectively, and theauxiliary contact structures 44b and 440 comprise stationary auxiliarycontacts 48b and 480, respectively. A reciprocably movable bridge 56a isprovided having movable main contacts 76b and 76c and having movableauxiliary contacts 78b and 780. Two platform castings 26b and 260 areprovided from which the main and auxiliary interrupters depend.

When the circuit breaker is in the closed position shown in FIG. 8, anoutermost and longer first U-shaped circuit is established from platformcasting 26b, through contacts 401) and 76b, through bridge 56a, andthrough contacts 76c and 40c, to platform casting 26c.

Furthermore, an innermost and shorter second U- shaped circuit isestablished from plat-form casting 26b, through contacts 48b and 78b,through bridge 56a and through contacts 78c and 48c, to platform casting260.

It is to be understood that the auxiliary contacts in the auxiliarycontact structures 78b and 78c are adapted to open before and closeafter the main contacts in the main arc interrupters 36b and 360.

If preferred, suitable shunt resistors could be employed with theembodiment disclosed in FIG. 8.

Assuming that the circuit breaker is closed as shown in FIGS. 1 and .5and that a fault occurs which causes it to open, the following sequenceof operations occurs.

Rod 57 moves cross bar 56 downwardly thereby causing all the movablecontacts and contact operators on the cross bar to start theirwithdrawal. As FIG. 6 shows, the contacts in the inner path, i.e., thosecontacts in the auxiliary contact structures 44, 46, 44a and 46a, openshortly before the contacts in the main interrupters 36, 38, 36a and38a. All current flow is now carried by the outer path. As cross bar 56continues to move downwardly, the contacts in the main interrupters 36,38, 36a and 38a open simultaneously and the impedances 52, 54, 52a and54a, respectively, are then connected in parallel with the arcs producedin the main interrupters to equalize circuit recovery voltage across themain interrupters upon opening. By the time cross bar 56 moves to thefully open position shown in FIG. 7, the arcs are extinguished and thecurrent flow through the impedances ceases since the movable contacts 58and 60 are disengaged from the sliding contacts in the lower castings 30and 30a.

More specifically, as regards operation of auxiliary interrupter 44,during the initial portion of the opening stroke of auxiliary bayonetcontact 78 is also accelerated by the forces exerted downward againstthe tip thereof by both piston push rod spring 112 and the piston spring114. However, after a fraction of an inch of piston stroke, the loweredge of piston ring 105 seals off the bottom of the refill ports 102.After this occurs, any further downward motion of piston 104 and pistonring 105 can be accomplished only by displacement of the oil in topsection 100 of structure 44. At this point, the velocity of the pistonis very greatly reduced since the limited area of orifice 124 betweenbaffie plate 122 .and moving auxiliary bayonet contact 78 allows verylittle oil to fiow out of structure 44 as long as auxiliary bayonetcontact 78 penetrates the baffie plate.

However, during the opening stroke the travel of piston push rod 110 isnot hindered by the travel of piston 104 nor is the spring force actingon the piston push rod in any way reduced by piston travel as is thecase in US. Patent No. 3,076,080 to J. M. Ramrath Fluid BlastInterrupting Device for Oil Circuit Breakers Employing AuxiliaryContact. Thus, when the velocity of piston 104 is reduced by theimpedance of the oil beneath it, piston push rod 110 continues to bedriven downward by piston push rod spring 112. Piston push rod 110continues to accelerate auxiliary bayonet contact 78 even after theelectrical separation of the auxiliary contacts. This follow throughaction terminates only when the flange at the upper end of piston pushrod 110 comes into contact with the top of the stationary contacthousing .116 to prevent any further push rod travel. At this point, thelower end of piston push rod 110 approaches the upper surface of baffleplate 122, forming a relatively small annular orifice between the bottomend of the piston push rod and the upper surface of the bafile platethrough which oil from auxiliary interrupter 44 may flow, and throughwhich any are between the stationary auxiliary contacts and the movingauxiliary contact must pass. The piston push rod stroke is terminatedonly after the auxiliary contacts have developed an appreciableseparation, approximately 4" in an actual embodiment. In this mannerauxiliary bayonet contact 78 receives an accelerating force from pistonpush rod spring 112, suificient to assure that the velocity of.auxiliary bayonet contact 78 does not fall below that of bayonet 76 ininterrupter 36. It also assures electrical separation of the auxiliarycontacts 48 and 78 at a precisely controlled period of time before theassociated main contacts 40 and 76 of main interrupter 36. This assuresthat the gap etween the auxiliary contacts will at all times be greaterthan the corresponding gap between the main contacts which areelectrically in parallel. As the piston continues to be driven downwardby the force generated by the piston spring, it pressurizes the oilbeneath it. The oil pressure drives the oil inward toward the lower tipsof the stationary contact fingers 118 and thence through annular orifice124 and out into the tank. As the oil is forced through orifice 124, itimpinges on any are which may tend to persist between the auxiliarycontacts 118 and 78 after their separation. This action subjects the arcto an oil blast which causes a turbulent mixture of the arc plasma withthe cold oil driven in from the cylinder. The resulting deionization ofthe arc products causes a rapid extinction of the arc. After the arc isextinguished, the continuation of a flow of fresh oil through orifice124 flushes any gas from the gap between the auxiliary contacts 48 and78 assuring the maintenance of a high dielectric strength of the gap.

On reclosing of the circuit breaker under load from the position shownin FIG. 7, the contacts in the auxiliary con tact structures 44, 46, 44aand 46a must close within one quarter of a cycle of the contacts in themain interrupters 36, 38, 36a and 38a in order to distribute the loadand to prevent high magnetic blowotf of the main contacts as the maincontacts continue to close. The main contacts continue to move to finalclosed position after the auxiliary contacts are closed.

As auxiliary bayonet contact 78 penetrates hole 124 in baffle plate 122,it is guided into axial alignment with the cluster of stationarycontacts to minimize bouncing of the fingers when contact is made. Theupper tip of auxiliary bayonet contact 78 comes into physical contactwith the lower end of piston push rod 110. As it continues its upwardmovement, it drives piston push rod 110 upward thereby compressingpiston push rod spring 112. Piston push rod 110 also bears againstpiston 104 forcing it and piston ring 105 upward, compressing pistonspring 114. Immediately before electrical contact is established betweenthe auxiliary contacts 78 and 48, the parallel contacts 76 and 40 ininterrupter 36 are closed to establish the outer circuit thus minimizingarcing between the auxiliary contacts. Further protection againstauxiliary contact deterioration can be provided by the application of asilver-tungsten alloy on the tips of the contact fingers 118. At the endof the closing stroke, piston 104 is driven upward beyond the refillports 102 in the side of top section 100. This allows any gas fromprevious interruptions to escape and also allows the oil to establishconvection currents for effective cooling of the auxiliary contactstructure while carrying heavy continuous currents.

It is to be understood that the embodiment of the invention shown inFIG. 8 operates in substantially the same manner as that described inconnection with FIGS. 17, except that only one pair of main interruptersand one pair of auxiliary contact structures are involved.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In an electric circuit breaker,

a pair of spaced apart line terminals,

a pair of electrically conductive upper platforms,

each upper platform being mechanically supported on and electricallyconnected to one of said line terminals,

a pair of upper main arc interrupters,

each upper main arc interrupter having a stationary main contacttherein,

each upper main arc interrupter being mechanically supported on one ofsaid upper platforms and having its stationary main contact electricallyconnected to its respective upper platform,

a pair of upper auxiliary arc interrupters,

each upper auxiliary arc interrupter having a stationary auxiliarycontact therein,

each upper auxiliary arc interrupter being mechanically supported on oneof said upper platforms and having its stationary auxiliary contactelectrically connected to its respective upper platform,

a pair of electrically conductive intermediate platforms,

each intermediate platform being mechanically supported by andelectrically insulated from one of said upper platforms,

a pair of lower main arc interrupters,

each lower main arc interrupter having a stationary main contacttherein,

each lower main arc interrupter being mechanically supported on one ofsaid intermediate and having its stationary main contact electricallyconnected to its respective intermediate platform,

a pair of lower auxiliary arc interrupters,

each lower auxiliary arc interrupter having a stationary auxiliarycontact therein,

each lower auxiliary arc interrupter being mechanically supported on oneof said intermediate platforms and having its stationary auxiliarycontact electrically connected to its respective intermediate platform,

a pair of upper movable main contacts for cooperation with saidstationary main contacts in said pair of upper main arc interrupters,

each upper movable main contact being slidably mounted on andelectrically connected to one of said intermediate platforms andnormally biased to open position,

a pair of uper movable auxiliary contacts for cooperation with saidstationary auxiliary contacts in said pair of upper auxiliary arcinterrupters,

each upper movable auxiliary contact being slidably mounted on andelectrically connected to one of said intermediate platforms andnormally biased to open position,

an electrically conductive bridge movable to open and closed positionsand having a pair of movable main contacts for cooperation with saidlower stationary contacts and a pair of movable auxiliary contacts forcooperation with said lower auxiliary stationary contacts,

said bridge also having a pair of upper main contact operators and apair of upper auxiliary contact operators,

and means for operating said bridge so that when said bridge is moved toclosed position, the movable main contacts engage their respectivestationary main contacts before said movable auxiliary contacts engagetheir respective stationary contacts,

and being further adapted so that when said bridge is moved to openposition, said movable auxiliary contacts disengage from theirrespective stationary auxiliary contacts before said movable maincontacts disengage from their respective stationary main contacts.

2. A circuit breaker according to claim 1 wherein when said bridge is inclosed position a first U-shaped circuit is established through saidmain arc interrupters and said bridge which is longer than a secondU-shaped circuit through said auxiliary arc interrupters and saidbridge.

3. In an electric circuit breaker,

a line terminal,

an electrically conductive upper platform mechanically supported on andelectrically connected to said line terminal,

an electrically conductive intermediate platform mechanically supportedby and electrically insulated from said upper platform,

an electrically conductive lower platform mechanically supported by andelectrically insulated from said intermediate platform,

an upper main arc interrupter and an upper auxiliary arc interruptermechanically supported on said upper platform,

each of said upper interrupters having a stationary contact thereinwhich is electrically connected to said upper platform,

a lower main arc interrupter and a lower auxiliary arc interruptermechanically supported on said intermediate platform,

each of said lower interrupters having a stationary contact which iselectrically connected to said intermediate platform,

an upper movable main contact and an upper movable auxiliary contact forcooperation with said stationary contact in said upper main arcinterrupter and said upper auxiliary arc interrupter, respectively,

each of said upper movable contacts being slidably mounted on andelectrically connected to said intermediate platform and movably biasedout of engagement from their associated stationary contacts,

a first resistor electrically connected between said upper andintermediate platforms,

a second resistor electrically connected between said intermediate andlower platforms,

an electrically conductive bridge movable to open and closed positionsand having a lower movable main contact and a lower movable auxiliarycontact thereon for cooperation with the stationary contacts in saidlower main arc interrupter and said lower auxiliary arc interrupters,respectively,

said bridge also having an upper main contact operator and an upperauxiliary contact operator,

and means for operating said bridge so that when said bridge is moved toclosed position said lower movable main contact first establishescontact with said lower platform to insert said first and secondresistors in circuit, then said upper and lower movable main contactssimultaneously engage said upper and lower stationary main contacts,respectively, and then said upper and lower movable auxiliary contactssimultaneously engage said upper and lower stationary auxiliarycontacts, respectively,

and so that when said bridge is moved to open position said upper andlower movable auxiliary contacts simultaneously disengage from saidupper and lower stationary auxiliary contacts, respectively, then saidupper and lower movable main contacts simultaneously disengage from saidupper and lower stationary main contacts, respectively, and then saidlower movable main contact disengages from contact with said lowerplatform.

References Cited UNITED STATES PATENTS 3,017,480 1/ 1962 Klaassen200--146 3,259,725 7/1966 Harper 200-150 592,497 10/ 1897 Scott 200-146977,577 12/ 1910 Wikander 200--146 2,792,476 5/ 1957 Cushing 200-1462,977,446 3/1961 Baker 200148.2 X

FOREIGN PATENTS 489,082 7/1928 Germany.

72,321 5/ 1916 Switzerland.

ROBERT S. MACON, Primary Examiner.

US. Cl. X.R. 200144

